Balanced tunable helical monopole antenna

ABSTRACT

This disclosure deals with a novel balanced tunable helical monopole antenna, that, through a symmetrical construction involving a central feed and simultaneous turn-shorting tuning from the ends thereof, enables the obviating of the necessity for a ground plane.

United States Patent Inventors Appl. No.

Filed Patented Assignee Ivan M. Faigen Cochltuate, Mme

Valor C. Smith, La Mesa, Calif.

852,052 Aug. 21, 1969 Nov. 23, 1971 Chu Associates, Inc.

Harvard, Mass.

BALANCED TUNABLE HELICAL MONOPOLE ANTENNA 4 Claims, 2 Drawlng Figs.

US. Cl

Int. Cl H0lq use Fleld 01 Search Primary Examiner-Eli LiebermanAttorney-Rines and Rines ABSTRACT: This disclosure deals with a novelbalanced tunable helical monopole antenna, that, through a symmetricalconstruction involving a central feed and simultaneous turn-shortingtuning from the ends thereof, enables the obviating olthe necessity fora ground plane.

PATENTEDuuv 23 I9?! H G 2 INVENTORS IVAN FAIGEN VALORQS M ITH m w uATTORNEYS BALANGED TUNABLE HELICAL MONOMLE ANTENNA The present inventionrelates to helical antennas, being more specifically directed to tunablehelical monopoles and the like.

In prior Us. Letters Pat. No. 3,235,871, issued Feb. 15, i966 to Lan JenChu et al., a successful tunable helical antenna is disclosed operablewith a ground plane. There are occasions, however, as when the antennasare to be used on small vehicles and the like which are to serve as theground plane, that such operation introduces aberration into the patternbecause the dimensions of such structures are an appreciable portion ofthe wavelength of an operating frequency or are otherwise too small topermit efi'ective operation as a ground plane. Matching problems arealso introduced since a small ground surface does not permit thematching attainable with an efiectively infinite ground plane. At lowfrequencies, moreover, particularly for location on masts and the like,sizable ground planes are bulky and often impractical.

It is to the objective of providing a new and improved helical antennathat shall not be subject to such ground-plane limitations anddifficulties, accordingly, that the present invention is primarilydirected; it being an object of the invention to provide a new andimproved helical antenna of the monopole type.

A further object is to provide a novel and balanced antenna of moregeneral utility, as well.

Other and further objects will be hereinafter set forth and are moreparticularly pointed out in the appended claims.

In summary, the invention contemplates a helical antenna windingcentrally fed and provided with a pair of similar terminal antennaelements, one connected to each end of the helical winding and eachprovided with shorting means for contacting the turns of the helicalwinding thereadjacent; the system being provided with means at each endfor synchronously rotating shorting means around the helical windingtowards or away from the center of the helical winding to tune theantenna.

The invention will now be described with reference to the accompanyingdrawing FIG. 1 of which is a schematic circuit diagram illustrating theinvention in preferred form; and

FIG. 2 is a similar view of the modification.

Referring to FIG. 1, a helical monopole antenna winding is shown at 1having an upper portion 1 and a lower portion 1", symmetricallysubstantially identical. Connected to each end of the two winding halvesl' and l" are shown cylindrical terminal dipole antenna elements 2 and2' preferably in the form of top hat or can"-type housings electricallyconnected with respective upper and lower ends of the helical winding 1.

Connected with these terminal elements 2 and 2 are shorting fingers,schematically illustrated at 3 and 3', respectively, which, in responseto the rotation of, for example, an internally disposed insulating screwor other threaded member 5 to which they may be mechanically secured,are caused to move synchronously both towards the center of the helicalwinding 1 or away from the same, as in response to the driving action ofa motor M which may, if desired, be contained within the element 2. Thefingers 3 and 3' will thus synchronously effectively shorten or lengthenthe respective helical winding halves l and l" to tune the same. Othertypes of ganged symmetrical shorting elements may similarly be used.

In this antenna, radiation is effected or received in the normal mode;that is, with a radiation pattern extending in a plane normal to thewinding axis along which the member 5 is disposed. This is showneffected by means of a feed loop 7, connected to the feed transmissionline 9, and illustrated in the fonn of a coupling, as described in saidLetters Patent, though other types of central symmetrical feeding mayalso be employed.

Under such circumstances, particularly with the cross dimension of theterminal elements 2 and 2' approximately the same as (preferablyslightly somewhat larger than) the turn diameter or cross section of thehelical winding 1, it has been found that the antenna may be operatedover wide tunable frequency ranges without the necessity for a groundplane' and thus, the antenna becomes entirely useab c with smallvehicles, masts and other structures where such structures themselvesserve as ineffective ground planes, as before discussed.

A somewhat similar structure is illustrated in FIG. 2, more particularlyadapted for horizontal operation, wherein, again, the elements 3 and 3'are ganged to move synchronously, inwardly and outwardly, symmetricallyand simultaneously to tune the two equal halves l' and 1" ofthe helicalwinding 1. In this embodiment, the dipole extensions 20 and 20' areshown in the form of linear elements extending substantially parallelwith winding axis and, indeed, if desired, in the form of wire dipoleradiators which may support the helical winding.

As an example, a monopole of the type illustrated in FIG. 1 has beensuccessfully operated over the wide band from 17 MHz. to about MHz. withan overall antenna length of about 21 inches and a helical windinglength of about 10 inches, with a helical turn diameter or winding crossdimension of about 3 inches.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within the spirit and scope of the inventionas defined in the appended claims.

What is claimed is:

1. A balanced tunable helical monopole antenna which obviates the needfor a ground plane, having, in combination, a continuous helicalmonopole winding, means for feeding the winding disposed centrallythereof such that the radiation pattern of the helical winding extendsin a plane normal to the winding axis, a pair of similar terminalantenna elements, one connected to each end of the helical winding andeach provided with shorting means for contacting the turns of thehelical winding thereadjacent, and means for synchronously adjustingsaid shorting means towards and away from the center of the helicalwinding to tune the antenna.

2. An antenna as claimed in claim 1 and in which said terminal elementsare dipole elements.

3. An antenna as claimed in claim 2 and in which said dipole elementsare cylindrical devices of cross dimension comparable to that of thehelical winding.

4. An antenna as claimed in claim 1 and in which said terminal elementsare linear elements extending substantially parallel with the saidwinding axis.

1. A balanced tunable helical monopole antenna which obviates the needfor a ground plane, having, in combination, a continuous helicalmonopole winding, means for feeding the winding disposed centrallythereof such that the radiation pattern of the helical winding extendsin a plane normal to the winding axis, a pair of similar terminalantenna elements, one connected to each end of the helical winding andeach provided with shorting means for contacting the turns of thehelical winding thereadjacent, and means for synchronously adjustingsaid shorting means towards and away from the center of the helicalwinding to tune the antenna.
 2. An antenna as claimed in claim 1 and inwhich said terminal elements are dipole elements.
 3. An antenna asclaimed in claim 2 and in which said dipole elements are cylindricaldevices of cross dimension comparable to that of the helical winding. 4.An antenna as claimed in claim 1 and in which said terminal elements arelinear elements extending substantially parallel with the said windingaxis.